Impurity-induced changes of overlayer symmetry and of phase transitions

Abstract

We show in a Low Energy Electron Diffraction (LEED) experiment that small concentrations of oxygen atoms (2 to 12% of a monolayer) added to half a monolayer of Sr on Mo(112), ordered in a c(2 × 2) structure, do not destroy order, but introduce new correlations with different translational symmetry. Thus incommensurate structures with domain walls are formed and the c(2 × 2) is finally transformed into a p(2 × 1) structure. Temperature-driven transitions at constant average densities from incommensurate to short-range order and finally to long-range order at high temperature can be described by simultaneous melting and domain wall evaporation.